One study says a daily nap cuts the risk of cognitive decline roughly in half. Another says people who nap a lot are more likely to develop Alzheimer’s disease.
Both are right. What separates them is the length of the nap.
The line falls at about 30 minutes
Researchers in Niigata, Japan, followed 389 people aged 65 and over for five years (Kitamura et al. BMC Geriatrics. 2021;21:474). Those who napped 1 to 29 minutes a day had 0.47 times the odds of cognitive decline (a drop of three or more points on a standard dementia screening test) compared with people who did not nap at all. That figure was adjusted for age, sex, chronic disease, drinking, smoking, and nighttime sleep. In the 30-to-59-minute group the advantage disappeared. In the 60-minutes-and-over group, 40.6% declined, versus 28.8% of non-nappers. That last difference did not reach statistical significance, but it points the other way.
It is a small study, and nap times were self-reported. On its own it settles nothing.
What makes it hard to dismiss is that heart research draws the line in the same place. A team at the University of Tokyo pooled 11 prospective cohort studies covering 151,588 people (Yamada et al. Sleep. 2015;38(12):1945-1953). People who napped 60 minutes or more a day had 1.82 times the risk of cardiovascular disease and 1.27 times the risk of death from any cause, compared with non-nappers. Under 60 minutes, neither risk rose. The dose-response curve was J-shaped: risk fell from zero to 30 minutes, then climbed, sharply after about 45 minutes.
Brain and heart. Different researchers, different diseases, same 30-minute mark.
Cause, or early warning?
This is where it pays to slow down. Do long naps cause disease, or does the disease, already under way, make naps longer? Observational studies cannot tell those apart.
A joint Harvard and UCSF study took that question head-on (Li et al. Alzheimer’s & Dementia. 2022; doi:10.1002/alz.12636). The team gave 1,401 older adults in Chicago, average age 81, a wrist-worn activity monitor for up to 14 days every year, counting long stretches of daytime stillness as naps. Follow-up ran as long as 14 years.
The relationship ran both ways.
Even among people whose cognition stayed normal, daily napping grew by about 11 minutes a year. After a diagnosis of mild cognitive impairment the increase jumped to 24 minutes a year, and after an Alzheimer’s diagnosis to 68 minutes. In the other direction, among people who started with normal cognition, those napping more than an hour a day had a 40% higher risk of developing Alzheimer’s than those napping less than an hour.
So a long nap is both a consequence of the disease and a signal that precedes it. The authors themselves say the evidence is not strong enough to conclude that napping causes cognitive aging. I want to be plain about that.
A separate study of 2,751 older men followed for 12 years found that those napping 120 minutes or more a day had 1.66 times the odds of developing cognitive impairment compared with men who napped under 30 minutes (Leng et al. Alzheimer’s & Dementia. 2019;15(8):1039-1047). Same direction.
Japan’s official sleep guide agrees
Japan’s Ministry of Health, Labour and Welfare published its Sleep Guide for Health Promotion 2023 in February 2024. For older adults it recommends avoiding long daytime naps and staying active during the day. It also suggests keeping total time in bed under eight hours. The reasoning: lying down for long stretches when you are not sleepy carries its own health risks.
What to actually do
Here is my own view, and only that: you do not have to give up naps. Just set an alarm. That one habit keeps you on the medicine side of the line.
Early afternoon, in a chair or on the couch, about 20 minutes. Getting into bed makes it easy to slide into deep sleep and blow past 30 minutes. And skip late-afternoon naps so they don’t eat into your night.
Naps that grow longer without you deciding it are a different matter. Sleeping an hour in front of the TV several times a week, or feeling drowsy all day despite a full night’s sleep, can sit on top of sleep apnea, medication side effects, depression, or early cognitive change. Don’t self-diagnose. Talk to your doctor.
Nap length is a readout on your brain and your heart, and it is about as easy to check as stepping on a scale.
The sleep chapter of my book Walking to 110 covers this alongside the seven-hour night and bedroom temperature.
Walking to 110: Japan’s Gift to the World for a Long, Healthy Life (Kindle)
References
- Kitamura K, Watanabe Y, Nakamura K, et al. Short daytime napping reduces the risk of cognitive decline in community-dwelling older adults: a 5-year longitudinal study. BMC Geriatrics. 2021;21:474.
- Yamada T, Hara K, Shojima N, Yamauchi T, Kadowaki T. Daytime napping and the risk of cardiovascular disease and all-cause mortality: a prospective study and dose-response meta-analysis. Sleep. 2015;38(12):1945-1953.
- Li P, Gao L, Yu L, et al. Daytime napping and Alzheimer’s dementia: a potential bidirectional relationship. Alzheimer’s & Dementia. 2022. doi:10.1002/alz.12636
- Leng Y, Redline S, Stone KL, Ancoli-Israel S, Yaffe K. Objective napping, cognitive decline, and risk of cognitive impairment in older men. Alzheimer’s & Dementia. 2019;15(8):1039-1047.
- Ministry of Health, Labour and Welfare (Japan). Sleep Guide for Health Promotion 2023. Published February 2024.